1. Field of the Invention
The present invention relates to an insulation detecting device and an insulation detecting method of a non-grounded power source, and particularly to an insulation detecting device and an insulation detecting method which detects an insulation status between a voltage boosting circuit and a non-grounded direct-current power supply mounted in an electric propulsion vehicle.
2. Description of the Related Art
In recent years, an electric automobile and a hybrid car are mounted with a battery assembly (hereinafter, abbreviated as a “direct-current power supply”) as a compact direct-current power supply having a high electric power and a high output power, and an output voltage thereof is equal to or more than 200 V (volt). In addition, in order to increase efficiency in driving loads, there is provided a vehicle provided with a voltage boosting circuit to boost and supply a positive potential of the direct-current power supply to the loads. In the vehicle provided with the voltage boosting circuit, the output of the direct-current power supply (that is, a primary side of the voltage boosting circuit) and the output of the voltage boosting circuit (that is, a secondary side) both are electrically insulated from the vehicle in a non-grounded manner. The vehicle is not used as the ground of the direct-current power supply and the voltage boosting circuit. Therefore, in the vehicle having the voltage boosting circuit, a ground fault resistance between the direct-current power supply and the ground and a ground fault resistance between the secondary side of the voltage boosting circuit and the ground both are necessarily detected in order to monitor an insulation status of the direct-current power supply.
As an insulation detecting device which detects the ground fault resistance between the direct-current power supply and the ground and the ground fault resistance between the secondary side of the voltage boosting circuit and the ground, for example, there is an insulation status detecting device disclosed in Japanese Patent Application Laid-open No. 2011-17586. The insulation status detecting device disclosed in Japanese Patent Application Laid-open No. 2011-17586 is configured to measure a composited ground fault resistance formed by the ground fault resistance between the direct-current power supply and a ground potential and the ground fault resistance between the secondary side of the voltage boosting circuit and the ground.
In the insulation status detecting device disclosed in Japanese Laid-open Patent Publication No. 2011-17586, the ground fault resistance formed between the positive electrode on the secondary side of the voltage boosting circuit and the ground (a secondary side+ground fault resistance) and the ground fault resistance formed between the negative electrode of the direct-current power supply (corresponding to the negative electrode of on the secondary side of the voltage boosting circuit) and the ground (a secondary side−ground fault resistance) are connected in series between the positive electrode and the negative electrode on the secondary side the voltage boosting circuit through the ground. In addition, in a case where a potential according to a division of the secondary side+ground fault resistance and the secondary side−ground fault resistance is higher than the positive electrode potential of the direct-current power supply, a sneak current from the secondary side “+” ground fault resistance of the voltage boosting circuit to the positive electrode of the direct-current power supply through a flying capacitor is generated. Furthermore, there is provided a reversed polarity measurement circuit which connects the flying capacitor to be in the reversed polarity with respect to a measurement means and the ground in order to measure a charged voltage in the reversed polarity with respect to the flying capacitor due to the sneak current.
Therefore, there is provided a measurement means which measure the charged voltage at the time of a positive polarity in a case where the flying capacitor is charged through the positive electrode of the direct-current power supply, and a measurement means which measures the charged voltage at the time of a reversed polarity in a case where the flying capacitor is charged through the positive electrode on the secondary side of the voltage boosting circuit at the time of the reversed polarity. In other words, there is required a dual-system measurement means including a measurement means which measures a charged voltage charged without the sneak current and a measurement unit which measures a charged voltage of the reversed polarity charged by the sneak current. Furthermore, the reversed polarity measurement circuit including at least a diode, a resistor, and a switch is necessarily added, and ON/OFF control on the added switch and a switching operation of the measurement means corresponding to the ON/OFF control are also necessary. Therefore, there is a problem in that a circuit scale is increased and a load on control software is also increased.